The invention relates to a method and an apparatus for producing wells in the surface of a rotogravure cylinder.
Such a method and such an apparatus are known, for example, from WO-A-92/09399. There the rotogravure cylinder is rotated by a rotational drive at a constant rotational speed and is processed by a laser light source so that wells are produced in its surface. The laser beam emitted as a continuous wave is pulsed by a laser control and is controlled in its power. A processing head, comprising a mirror, an optoacoustic modulator and an optical lens, is moved along the rotogravure cylinder. The pulsed laser beam is deflected by the mirror and adjusted by the optoacoustic modulator to correspond to the rotational speed, and directed in a specific processing mode onto the surface of the rotogravure cylinder. The optoacoustic modulator is likewise controlled by the laser control. It is pointed out specifically that it is hardly possible to carry out processing of adjacently located wells since breaches to the adjacent well can occur due to the intense local heating of the cylinder surface. For this reason, a processing mode is proposed, in which the laser beam is deflected by the optoacoustic modulator in such a way that, for example, starting from a hollowed-out well, firstly two intended wells are missed out forwards and the following well is hollowed out, and then two intended wells are missed out backwards and the following well is hollowed out. The hollowed-out wells have thus cooled down sufficiently to produce an adjacent well without breaches in the wall. In the event of the energy being insufficient to hollow out a relatively large well, the laser beam is directed onto it again subsequently after cooling. The person skilled in the art can assume from all these tasks that the rotational speed of the rotogravure cylinder must be relatively slow and the processing time for an individual well must be relatively long.
The present invention is based on the object of specifying a method and a device for producing wells in the surface of a rotogravure cylinder, which allow far more rapid processing of directly adjacent wells.